In many gas turbine engines, the fuel system for regulating the flow of fuel to the combustion chamber consists of one or more fuel nozzles arranged in the combustion chamber, a fuel pump for pressurizing fuel from the fuel supply, a fuel metering unit for controlling the flow of fuel to the fuel nozzles and one or more fuel manifolds fluidically connecting the fuel metering unit to the fuel nozzles.
During engine start-up, fuel is pumped from the fuel supply to the fuel metering unit by the fuel pump and, once a sufficient start-up pressure is attained, the pressurizing valve of the fuel metering unit opens and fuel is supplied to the fuel nozzles via the fuel manifold. Thereafter, the metering valve of the fuel metering unit modulates the rate of fuel flow from the fuel supply to the nozzles. As such, a single, continuous flow path exists from the fuel metering unit, through the fuel manifold, to the fuel nozzles.
When the engine is shutdown, residual fuel may remain in the engine manifold. It is desirable to prevent the residual fuel from remaining in the engine manifold to prevent coking of the residual fuel. Coking of the residual fuel is a fire hazard and can lead to blockages in engine fuel injectors, which results in shorter injector life and can harm engine performance.
It is known in the art to drain residual fuel from the manifold of an engine, downstream of the engine shutoff valve, to prevent the fuel from coking. U.S. Pat. No. 6,442,925 to Dalton et al. discloses a system for draining residual fuel from the engine manifold of a gas turbine. The system includes an ejector having an inlet port for receiving high pressure fuel from a main fuel pump at engine shut-down, an outlet port and a suction port. The ejector defines a nozzle that extends between the inlet port and the outlet port for increasing the velocity of high pressure fuel flowing therethrough at engine shut-down so as to create suction at the suction port. A motive valve controls the flow of high pressure fuel between the main fuel pump and the inlet port of the ejector. A drain valve controls the flow of residual fuel between the engine manifold and the suction port of the ejector such that residual fuel is drawn from the engine manifold under suction to the inlet port of the ejector.
While the Dalton patent provides a unique system for pumping the residual fuel from an engine manifold after the engine is shut down, it is a relatively complex system. The motive valve and drain valve require simultaneous operation. The simultaneous operation is controlled by a three-way shutoff solenoid valve that is used to simultaneously control the motive valve and drain valve. These features add to the overall complexity and may decrease the reliability of the system. Accordingly, there is a need for an improved engine manifold drain system which overcomes the deficiencies of prior art systems.
The invention provides such an improved engine manifold drain system. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.